Small Engines (Lawn Mowers, etc.): restart a diesel after it runs out of gas, wd 40, diesel engine

Question
I have a cub cadet tractor with a diesel engine. My son ran it out of gas and I can't get it restarted. The battery goes dead.. Is there a trick to it? It's sitting in the backyard in the shade, do I need to warm it up? It's been two days now. Gets down in the 50's at night...please help, thanks,

Answer
most have a lever on the fuel pump to prime it, it takes a while so be patient the manual should give you instructions on starting after loss of fuel. or my method because its easier is sraying a can of wd-40 in the air intake while cranking, it should start, and after a minute or two will take off on its own without the spray